Mercury relay



June 30, 1942. u. c. HEDIN MERCURY RELAY Filed May 6, 1940 5 Sheets-Sheet 1 /l //V///////E INVENTQR: [/72 0 BY WZ l ATTORNEY.

ww. 1% uw NN s@ June 8o, v1942. U. @,-HEDIN 2,288,089

MERCURY RELAY ,Filed May 6, 1940 5 Sheets-Sheet 2 INVNTOR.

ATTORNEY.

Uno (AJ/@Z198 u. c. HEDIN MERCURY RELAY June 3), 1942.

3 Sheets-Sheet 3 Filed May 6, 1940 INVENTOR. y [//20 zedi Www/5MM ATTORNEY.

Patented Jane 30, 1942 srAres PATENT orrice MERCURY RELAY Uno C. Hedin, Elkhart, Ind., assigner to Bucklen- Bear Laboratories, Inc., Elkhart, End., a corporation cf Indiana Application May 6, 1940, Serial No. 333,533

i (ci. zoog-cr) 24 Claims.

. in which a plunger or displacer is magnetically controlled to change the mercury level in the relay for controlling the opening and closing or" a circuit through the relay. In the present form of invention a metal envelope type of relay is vemployed wherein the envelope itself may, in

several embodiments of the invention, directly form the one electrode of the relay and has an insulating bushing sealed in one end of the envelope which in turn carries a second electrode between which contact is made and broken by the liquid contactar comprising mercury.

In the present invention I have departed from my copending disclosure referred to above in providingfor time control of the making and breaking of contact in such manner that I may byA providing spacers or prongs on the ends of the plunger, this will not occur, and that the plunger, if provided with this type of end structure, can have the lateral guides eliminated and still no sticking will be produced, since, if the annular space between 'the plunger and the intemal wall of theenvelope is kept suflciently small so that no. mercury can enter therebe- 1 the plunger is greatly increased by having no provide for a slow make and slow break of contact in the relay even though the displacer moves rapidly when the magnetic coil is energized, or I may provide for a combination fast make and slow break, or various combinations of time delay or time control in the making and breaking of the circuit, whereby the relayv may be made adaptable to a variety of us'es not possible with the ordinary type of fast' make and fast break.

In this connection I have provided novel types of relay switches embodying certain features, which allow very accurate control of the making and breaking of the circuit so that the time delay canbe built into the relay and it will al ways operate under the desired conditions.

Still another feature of the present invention is the provision of a novel type of plunger construction whereby the displacer is provided with lugs on the ends of the plunger. I have found that under certain conditions there has been a tendency for the plunger to stick in position, and whilev this has been in general attributed to binding or clamping of the plunger in the bore of the envelope, I have discovered that this is not the major cause of the plunger sticking, but that the adhesion of the lower end of the plunger to the mercury in the bottom of the envelope produces a sealing effect which prevents the plunger from rising. I have discovered that tween, the plunger will slide freely, and the action will be as good or better than if lateral guides were employed. This has a certain distinct value since the physical air gap is reduced, thereby reducing the reluctance or magnetic re sistance which is a function of such air gap,

and thus the amount of current necessary for actuating the plunger can be reduced. Furthermore, the displacement per unit movementI of mercury layer surrounding the plunger. This is of special importance when a normally closed contact is used since the plunger is lifted magnetically and dropped by gravity. Thus, with such a plunger construction less current is required in the solenoid to operate the plunger, the cost is reduced in manufacturing the plunger, and a smaller amount of mercury is required.

Another feature of the present invention is to provide an envelope which is made of an austenitic steel or of a nonmagnetic material, which reduces the reluctance or resistance between the magnetic coil and the plunger.

In certain cases, however, it is desired to use a plunger in which the mercury can pass upwardly along the outside of the plunger, and. in one form of the invention, a plunger of this type is desired in order to provide a quick make, slow break type of relay. In such event, I preferably provide a plunger of a polygonally shaped steel rod, whereby advantage can be taken of the natural iluting eifect to provide passageways for mercury between the corners on the external surface of the plunger. If desired, the rods may be turned down intermediate the ends, leaving only the polygonal guides at the ends of the plungers.

Another primary object of the present invention is to provide a magnetic relay of this type in which the major portion of the parts can be of the same type as used in mercury switches of the type shown in the Paul S. Bear Patent #2,132,921, issued October 11, 1938.

Another feature of the present inventionresides in the provision of a relay construction in which the two electrodes are telescoped, one withinthe other, in insulated relation, and the time delay is controlled by metering the ilow of mercury through a thin wall orice. I have dis,- covered that the thinner the wall surface the smaller the orifice through which mercury ,will

- pass, and consequently by controlling the wall.

thickness of one of the electrodes I can provide for accurately controlling the rate at which mercury will flow therethrough, and can therethe making and breaking of contact in a relay of this type.

Other objects and advantages of the present fore control the time delay interposedbetween invention will be more apparent from the following detailed description which, `taken in con- Figure 3 is a vertical sectional view throughv a relay employing telescoping electrodes; v Figure 4 is a detailed sectional view of a modi` flcation of the structure shown in Figure 3;`

Figure 5 is an end elevational view\oi`the, `plunger shown in Figure 3;

Figure 6 is a sectional view of the plunger shown in Figures 1 and 2;

Figure '7 is an elevational view of a modiiied form of relay structure in its open circuit position;

, Figure 8` illustrates the same relay as the coill is energized'to close the circuit; and

. Figure 9shows the relay of Figure rI as the coil is de-energized. f

Referring now in detail to the drawings, in

Figure l I have disclosed a metal envelope or shell 5 which has the enlarged open end 6 within which is disposed the refractory insulator 'I provided with the vertically extending elongated cylindrical tubular portion 8. Disposed within the bore of the tubular portion 8 is a thin metal sleeve 9 which, atits lower end, is adapted to engage a metallic electrode disc III seated in a recess in the insulator 'I and having a shank portion extending outwardly of the end 'of the envelope. A suitable resilient sealing'gasket I2 engages the radial face of the insulator I and has a short skirt portion I3 radially overlapping the annular periphery of the insulator. The gasket spills over the upper end of the tubular sleeve l displacer may be of a magnetic metal. the envelope 5 preferably being of a non-magnetic material, such as austenitic metal or similar material. The entire assembly is preferably enclosed within an insulating two-piece molded case having the body portion 21 and the lower cap portion '28 rabbetted therein. This assembly is held in any suitable manner within the center of a magnetic coil 29, similar to the manner described in my` copending application referred to above.

It will be noted 'that the sleeve 9, which, as heretofore stated is of very thin wall section, is provided with a small aperture substantially 1, the circuit is open, and upon energization of the coil 29 the plunger 28 is drawn downwardly providing for upward displacement of the body 8, this body of mercury rising .in height until it andlillls the upper end of this tubular sleeve to produce contact between the contact tip 22 of contact with the electrode I0, thus completing the circuit through the relay. When the coil is de-energized, the plunger 26 immediately moves upwardly and thereby lowers the level of the within the insulating tube 8 cannot escape except by flowing through the small orifice 3i). which kproduces a time delay until the mercury level in ing a much longer time delay than if the mercury were restricted by the ceramic hole.- The size of the aperture 30 determines the rate at which the level of mercury within the extension 8 will drop, and consequently determines the time delay be- 80 tweende-energization of the coil 29 and opening I2 is compressed into sealing engagement by vide a quick make, slow break with the length means of an insulating compression member I4 which is heldin position by means of the metallic retaining ring I5 secured under the spun-over edge I6 of the envelope. Adjacent the upper end of the envelope' 5 there is provided the annular bead I1, and seated against axial inward movement against this bead is an insulated bushing I8 adapted to receive the second electrode disc I9 which has threaded or otherwise suitably secured therein the electrode stem 28.

The projecting end Aof this stem is preferably provided with an arc-resisting ymetallic contact tip 22 which may comprise tungsten, or a similarl arc-resisting metal. The bushing I8 is, held lin position by means of a gasket 23 corresponding to the gasket I2 held in position by a corresponding compression member 24 located beneath the spun-over end 25 of the envelope.

Disposed within the envelope in telescoping relation to the tubular extension 8 of the insert 1 of the circuit between the electrode 22 and electrode III. It is therefore at once apparentthat with such .a construction the rate of operation of the relay can be accurately controlled to pro-I I of time between de-energization of the coil and opening of the circuit being controlled solely by the size of the aperture 30. Such relays are adapted to be connected to a control circuit, and such connections may be made through a conductor 35 connected to the projecting shank of the electrode I0 and conductor 39 connected to the projecting shank of electrode I9.

The relay shown in Figure 2 comprises an envelope 40 in which is disposed the insulating bushing 42 having an axially opening recess 43 adapted, when in inoperative position, to receive the upper end` of the displacer 44. Extending centrally inthe recess 43 the ceramic is provided with a tubular extension 45 which. at its lower end, is counterbored to receive a plug or disc 49 having the apertured bushing 4'I therein, the disc 46 being held in positionby the snap ring is a displacer, indicated generally at 28, which 48. It will be noticed that the disc- 46 and bushcentered with respect to a much larger aperture sleeve 9 and also with the of mercury 34 surrounding the tubular extension the electrode I9, and the body of mercury 33 in mercury 34 very rapidly. However, the mercury ing 41 are provided with oppositely extending frusta-conical recesses leading to the aperture to provide a thin walled section at the aperture for facilitating the passage of mercury therethrough. The diameter of the aperture and the thickness of the wall section defining the aperture determine the rate at which mercury will pass therethrough into the extension 45.

'I'he insulator 42 is held in fixed position within the envelope 40 by means of a resilient gasket 49 which is compressed in position by the compression insulator held in place by the spun-over edge 52 of the envelope. A suitable metallic ring 53 is clamped beneath the edge 52 of the envelope and is adapted to receive the terminal end of the conductor 54 leading outwardly from the relay through an aperture in the insulating case member 55. The compression member 50, against 49, and insulator 42 are suitably apertured to receive an electrode pin 56 which, at its upper end is adapted to be engaged by the conductor 51 and enclosed by the insulating cap member 58. The electrode 56 is provided with an extending portion terminating in the tip 59 disposed within and spaced from the walls of the tubular extension 45 of the insulator. The relay structure is adapted to be supported within the bore of Ian energizing coil 60, which coil when energized operates to draw the displacer 44 downwardly toward the closed end of the envelope 48. This results in displacing the mercury 6K2 upwardly, forcing a portion of the mercury to pass through the aperture in the bushing 41 and rising in the extension 45 until contact is made with the electrode tip 59, thereby closing the circuit between the 'conductors 54 and 51. i

Upon de-energization of the coil 68 the plunger '44 rises to the position shown in Figure 2, thereby causing the mercury level to drop.. The rate of drop of mercury around the extension 45 is much greater than through the apertured bushing 41, and consequently a time delay is interposed between de-energization of the coil 60 and actual breaking of the contact between the tip 59 and the body Yof mercury 63 carried within the extension 45.

It will thus be apparent that with this form of switch a time delay is interposed both in making and breaking the circuit through the relay, this time delay being controlled by the sides of the aperture and the wall section of the bushing 41.

The plunger in this form of the invention includes a ceramic sleeve 64, which is provided at one end with circumferentially spaced laterally extending projections or guides 65 over which is teiescoped a metal sleeve 66 which is provided with the laterally extending guides or bosses 61 whereby' laterally projecting guides are provided at both ends of the plunger. In addition, if desired, the plunger may be provided with axially directed prongs at the ends thereof, similar to the prongs 38 and 39 shown in Figure l.

In the form of the invention shown in Figure 3 a fast make slow break type of relay is provided in `which coaxial relatively insulated electrodes are provided, and the envelope is not included in the electric circuit. In this form of the invention the envelope i8 is provided with the insulating bushing 'i2 having the` central vertically extending cylindrical portion 13 open at its. upper end, the bore of the extension 13 extending through the bushing and being radially enlarged adjacent the outer end of the bushing to provide a seat for the enlarged portion 14 of an electrode 15. The electrode 15 is provided witha tubular shank portion 16 which projects outwardly below the lower end of the envelope, and at its outer end receives the terminal end of a conductor 18. At its opposite end the electrode 15 is provided with a cylindrical thin walled ange portion 1.9, which extends for a portion of the length of the extension 13 of the bushing and is provided with a transverse aperture 80 adapted to be alined with an enlarged aperture 82 formed in the side wall of the extension 13. These apertures correspond to the apertures 36 and 32 of Figure 1, and provided for metering the iiow of mercury therethrough from the interior of the extension 13 to the annular spacing surrounding this extension.

The electrode 15 is provided with an axial bore extending the full length thereof which is adapted to receive the rod-like electrode 83 which, about itsexternal surface, is provided with av coating of an insulating material 84 eiectively insulating the electrode 83 from the electrode 15. The insulation 84 terminates a short distance from the upper end of the electrode 83 to leave a" portion of the electrode extending as a contact terminal.

'I'he opposite en'd of the electrode is adapted to A be connected to the conductor 85 forming the opposite side of the `circuit through the relay. Mounted for axial-sliding movement within the cylindrical portion of the envelope 10 is a displacer comprising a ceramic sleeve 86 about which is wrapped a metal sleeve 81, the sleeve 81 having oppositely struck tongues 88 and 89 aty eachv end thereof. The tongues 88 project laterally and serve as guides for the plunger against the lateral walls of the envelope 1,8. The tongues 89 are bent over the opposite ends of the sleeve 86 to thereby retain `the sleeve 81 and sleeve 86 y against relative movement.

With the structure as shown in Figure 3, the relay is in open position, the body of mercury 98 being at the level indicated wherein that portion of the mercury Within the extension 13 is disposed below the upper end of the insulation 84. and consequently out of contact with the tip 83. Upon energization of the coil which surrounds the relay, the plunger 81 is drawn downwardly into the mercury body, causing this mercury body to flow over the upper end of the extension 13 into the interior thereof, thereby raising the level of mercury within the extension to a point Where it effects contact between the electrode 15 and the electrode tip 83 thereby closing the circuit between the conductors 18 and 85.

Upon de-energization of the coil, the plunger 81 immediately risesinto the positionshown in Figure 3, but the mercury Within the extension 13 must fall by passage outwardly through the oritice 80. Asv a result, its rate of movement is reduced with respect to the falling vlevel of mercury surrounding the extension, and consequently a time delay is introduced in opening the circuit through the relay. This time delay is controlled by the size of the -orice 80 and the thickness of the wall section 19, as described in connection with Figure `1.

In determining the type of insulation to be applied about .the electrode 83 for insulating it v from the electrode 15, it was nally determined cause of its resistance to thermal shock and because it softens at a higher temperature than.

soft glass, thus permitting better baking use for the gasification of parts.

I have found that `the vmetal best suited to use in connection with a glass insulation of this type is an iron nickel cobalt alloy which is sold under the trade name of KovarJ 'Ifhis metal readily seals-into hard glass toV- produce a permanently vacuum-tight seal. The metal also has the desired characteristic of resisting mercury arcs and may be easily machined, thereby permitting its use in various forms and shapes. In assembling the structure shown in Figure 3 the inner electrode 83 is first beaded with glass which is fused Considering the structure in detail, the metal envelope is provided having the insulating v Abushing |02 disposed therein and provided with on in re, and then the outer Kovar electrode is fused onto the glass bead. Inasmuch as thisstructure provides a positive vacuum-tight seal,

it is apparentl that the relay so constructed can be evacuated after the sealing gasket 98 and the compression member 94 have been secured in position by means of tubulation, such as the tubulation 95 at the upper end of the envelope in the same manner as is now employed in connection with normally tilt-operated mercury switches of the metal envelope type.

Referring now to the construction shown in Figure 4, this is a modification of the relay as I sembly of Figure 3 except that the tubular' extension 13 of the bushing 12 is provided at its upper end with a closing ange 96 provided with a small aperture 91. The plunger in this form of the invention comprises a ceramic sleeve 98 over which is slipped a metal sleeve 99, this sleeve preferably having an external diameter only slightly less than the internal diameter of the envelope ,10, wherebyian annular space is provided insufficient to al1owmercury to run therebetween. ,This eliminates the necessity of forming lugs or lateral bosses 88 as shown in Figure 3, since the small air gap will allow the plunger to oscillate freely within the 'enveope At the same time, it

brings the magnetic metal of the displacer much closer to the field of the electric coil, consequently reducing the air gap andthereby reducing the magnetic resistance or reluctance in the relay.

The' relay'l of Figure i is adapted to provide a slow make and break in that when the plunger 99 is drawn downwardly the mercury body 90 velope is thedisplacer H0. This displacer comprises a piece of hexagonal rod stock which has its upper end spun over the ceramic sleeve H2, the lower end of this sleeve being spaced from :the inturned shoulder H8 of the displacer to clamp therein the iron disc 4 provided with the restricted aperture H9. The extension |08 is provided with a vent hole H8 opening into the annular space in the extension about the electrede/tip |04. 'I'he envelope is adapted to be filled with a predetermined volume of mercury H1. In. operation, when the displacer is moved downwardly toward the'lower end of the envelope by energization of the coil 09, the mercury passes up the nat sides of the spacer about the lateral surface thereof overflowingthe top of the spacer and moving down into the interior of the spacer, and thence up into the extension |08 to contact the electrode |04. While I have shown the displacer' as being hexagonal in external form, this can be of anypolygonal form desired which will provide mercury passageways about the outer surface thereof to provide the spill-over effect for producing a rapid closing of the circuit between has its lever outside the extension 13 raised, but

the aperture 91 in the end 96 of the extension is of insuillcient diameter to allow the mercury to'run therethrough, and consequently the level in the interior of the extension raises slowly due to the-fact that the mercury must enter into the extension through the opening 82 in the extension and the aperture 80 in the metal sleeve 19. 'I'he aperture 91 is for the purpose only of providing a vent to allow free movement of the mercury within the extension 18. Similarly, when the coil is de-energized, the plunger 98 raises immediately. lowering the level of the mercury 90 about the extension 13 and the mercury within the vextension consequently is slowlyl lowered by draining through the apertures 80 and 82. Thus a relatively slow make and break is provided by the construction shown in Figure 4.

Considering now the form of -the invention shown in Figures 7 to 9, inclusive, a quick make slow break type of relay is provided with a structure which comprises a modification, to some extent, of the structure shown in Figure 2. In this form of the invention `the relay is shown in its unenergized position in Figure 'l and in its energized position in Figure 8. Figure 9 discloses the position of the parts after de-energization of the coil but prior to breaking of the circuit, and illustrates the manner in which the time delay is effected. v

the envelope and the electrode tip |04. The position of the displacer when in energized poistion is shown in Figure 8, wherein the mercury level is such as to aiiord contact between the electrode and the envelope |00. When the coil |09 is deenergized, the displacer immediately rises to the position shown in Figure 9, but it willbe noted that the mercury within the displacer is trapped therein and cannot escape from the interior of the displacer except through the orifice lli. As a result, the mercury drains at a Vslow rate through this orice to the level of the mercury around the outside-ofthe displacer, and consequently provides a delayed opening of the circuit through the relay, depending upon the size of the orifice H5 and the thickness of the wall deilning the orifice. .This can be accurately controlled to provide any desired time delay. With such a construction, it will therefore be apparent that the spill-over action to increase the rate at which the circuit isl made through the relay is limited onlyto the energizing cycle of the relay, and upon de-energization,V the spill-over action cannot affect the circuit of the relay because of the mercury trappedwithin the cuplike displacer, which must slowly be dissipated through the orifice ||5 through the lower end of the displacer.

It is therefore believed apparent that I have provided a novel type of time delay metal en-'- velope mercury relay having a number of disor a similar material, and in all forms of the invention except that shown in Figures 3 and 4. forms one portion of the electric circuit through the relay.

It will be obvious that the amount of time delay produced in the various forms of the invention can be readily varied by controlling the size of the metering aperture which drains the mercury away from the electrode and by the thickness of the wall section forming this aperture, since the thinner the wall the smaller the opening through which the mercurywill pass.

I am aware that various changes may be made in certain details of the construction and operation herein shown and described, and I therefore do not intend to-be limited except as defined by the scope and spirit of the appended claims.

I claim:

l. A mercury relay comprising a metal envelope having a ceramic insert providedwith an axial ltubular extension, an electrode extending partially through said extension, a plunger axially reciprocable in said envelope about said extension, a body of mercury in said envelope displaceable upon movement of said plunger-.to contact said electrode in said extension, and means for metering the now of said mercury out of contact with said plunger.

2. A mercury relay comprising a metal en- I velope having a ceramic insert in one end thereof provided with an axially inwardly directed tubular extension, an electrode disposed Within said extension, a displacer surrounding said extension, a body of mercury in saidenvelope about said extension, means for drawing said displacer downwardly into said mercury to displace the same over the upper end of said extension into contact with said electrode, and a metering orifice near the base of said extension for restricting drainage of mercury out of said extension.

3. A mercury relay comprising a vertical metal envelope having a ceramic insert in the lower end thereof provided with an axially upwardly place mercury over one end of the sleeve to i111 the same and effect contact between said electrodes in said sleeve, said electrodes extending through said sleeve in telescoping relation, and insulating means forming an annular separation therebetween. A

7. In a metal envelope mercury relay, a ceramic sleeve secured therein having insulatlngly spaced electrodes therein, one of said electrodes having a sleeve portion spaced radially about the other electrode, a displacer surrounding said sleeve, a body of mercury in the envelope, alined metering apertures in the side of said sleeve and said sleeve portion of said one electrode, and means for energizing said displacer to raise the level of mercury in 4said envelope and meter a portion of said mercury through said aperture to eiect mercury bridging contact between said electrodes within said sleeve.

8. The relay of claim 'I wherein said electrodes comprise coaxial metal stems of unequal length, with insulation therebetween.

9. A mercury relay comprising a metal envelope having a ceramic insert secured therein and provided with a tubular extension vented at its upper end, a pair of electrodes Within said extension, one of said electrodes being insulated from the other and extending vertically thereabove, a radial port in said extension adjacent the lower end thereof, a body of mercury in said envelope of a volume normally maintaining a level in and around said extension insumcient to directed tubular .extension open at the uppel end tween said electrodes within said extension.

4. The relay of claim 3 further characterized in the provision of lateral port means in said sleeve and extension metering the now of mercury out of said extension.

5. In a metal envelope mercury relay, a tubular ceramic sleeve extending axially'thereln, a

pair of coaxial electrodes extending into said sleeve in insulated relation and having the ends thereof apart axially, a body of mercury surrounding said sleeve, a displacer operable todisplace mercury over one end of the sleeve to fill the same and effect contact between said electrodes in said sleeve, and port means in said sleeve for metering the flow of mercury out of said sleeve to break contact between said electrodes;

6. In a metal envelope mercury relay, a tubular ceramic sleeve extending axially therein, a pair of coaxial electrodes extending into said sleevein insulated relation, and having the ends thereof apart axially, a body of mercury surrounding said sleeve, a displacer operable to disbridge between said electrodes in said extension, and a displacer operable to raise said level sumcient to effect bridging contact between said electrodes.

10. The relay of claim 9 wherein said port is of a size such as to retard the change of level within the extension to provide a predetermined time deiayafter operation of said relay before the mercury level within said extension becomes equal to that outside said extension.

1l. A displacer for a mercury relay comprising a short length of polygonal section metal rod having an axial bore therethrough terminating at one end in a radial inwardly directed flange. a transverse disc in said bore supported on said flange and having a thin central section provided with an axial aperture, and means in said bore locking said disc against axial movement relative to said rod.

12. In a metall envelope mercury relay, a ceramic insert secured in one end of the envelope and having a Vfixed tubular extension, an electrode in said extension terminating short of the .end thereof, a body of mercury in said envelope,

the end of said extension and'of varying axial thickness, and a port opening defined by the thinnest section of said disc controlling the rate of flow of mercury therethrough into contact vitl said electrode upon raising of said mercury eve 13.v In'combination, in a mercury relay, a metal envelope open at each end, an insulator sealed in each end of said envelope, one of said insulators having a tubular axial extension, an electrode, carried by each insulator extending toward each other and spaced apart within said extension, a body of mercury in said envelope, al port in said extension providing for metered flow of mercury therein, and a displacer surrounding said extension andoperable to raise the level of the mercury around said extension, said port providing for retarding the rate of' change of level in said extension.

y14:. The combination of claim 13 wherein /said extension has an open upper end over which the mercury.v is displaced into said extension tof` provide a quick making of circuit between said Selectrodes but said port delays lowering of the 'mercury level in said extension upon lowering of the upper end, a pair of insulated electrodes extending axially in said sleeve and terminating at different axial points below the open end of said sleeve, a body of mercurysurrounding said sleeve, and a displacer operable upon energization of said coil to displace mercury up over the upper end of said sleeve to fill the same for effecting contact between said electrodes.

16. The relay of claim 15 further characterized in the provision of a laterally opening port in said sleeve below the upper end of the lower electrode for metering the `flow of mercury out of said sleeve to delay the breaking of contact between saidelectrodes upon return of said displacer when said coil is deenergized. x'

17. A mercury relay comprising a tubular metal l envelope composed of austenitic steel, an actuat' ing coil surrounding saidl envelope, a pair of axially spaced electrodes disposed in sealed in-` sulated relation within said envelope, a body of mercury surrounding said electrodes and normally out of contact therebetween, and a paramagnetic displacer operable by said coil for raising said mercury to contact between said electrodes.

18. Inl a metal envelope mercury relay, a ceramic body member sealed in one/end of said envelope and having an axially projecting sleeve, an electrode within said sleeve terminating short of the upper end thereof, a second ceramic body in the provision of lateral portk means in said sleeve below the upper end of said rst electrode for draining said mercury in said sleeve at a vpredetermined rate to delay breaking of contact 22. A metal envelope mercury relay comprising a cup-shaped metal envelope having an enlarged open end, a ceramic sealed in said end and having a tubular axially projecting sleeve spaced radially within saidenvelope, a tubular displacer of a diameter such as to surround said sleeve and reciprocable in said envelope, a body of mercury normally lying in the closed end of said envelope and surrounding and filling the lower end of said sleeve. an electrode disposed in said sleeve and terminating short of the lower end of said sleeve, and an actuating coil surrounding said closed end of said lenvelope and operable to draw said displacer downwardly into the body of mercury for raising the levelthereof to effect contact between said electrode and said envelope.

23. The relay of claim 22 further characterized in the provision of a metering disc secured across the 4lower end of said sleeve for determining the time delay between operation of said coil and closing of said contact.

24. A metal envelope mercury relay comprising a tubular metal shell having a ceramic in one end thereof provided with an axially extending tubular sleeve closed at its upper end, means providing a vent port in said closed end of said sleeve,

\ apair of coaxial electrodes insulatingly spaced member sealedin the opposite end of said envelope and having an axial electrode extending into the open upper end of said sleeve short of upon operation of said displacer to illl said sleeve for effecting contact between said electrodes within said sleeve. l

- 19. The relay of claim 18 further characterized from each other extending into said sleeve, a lateral port in the lower end of said sleeve, a body of mercury in said envelope surrounding said sleeve and having. a portion thereof disposed in said sleeve, and a displacer operable to raise the level of mercury outside of said sleeve whereby the level within said sleeve is correspondingly raised to effect contact between said electrodes.

UNO c. HEDIN. 

